The present invention relates to one part heat curable organopolysiloxane compositions having improved shelf stability. More particularly, the present invention relates to the encapsulation of a palladium halide complex, such as CODPdCl.sub.2, where COD is 1,5-cyclooctadiene, with beta cyclodextrin (BCD) and the use of the resulting inclusion compound as a hydrosilylation catalyst.
Prior to the present invention, as shown by Kookootsedes et al., U.S. Pat. No. 3,445,420, one part heat curable organopolysiloxane compositions were based on a platinum catalyzed silicon hydride-silicon vinyl addition reaction which generally utilized an inhibitor for the platinum catalyst. The purpose of the inhibitor was to slow down the hydrosilylation reaction to increase the work life of the one component organopolysiloxane mixture at low or room temperatures. The organopolysiloxane mixtures were generally composed of a base polymer consisting of a polydiorganosiloxane having chemically combined methylvinylsiloxy units which was used in combination with a siliconhydridesiloxane. Additional inhibited one package silicon hydride-silicon vinyl one package platinum addition curable organopolysiloxane compositions are shown by Berger et al., U.S. Pat. No. 3,882,083, utilizing an ethylenically unsaturated isocyanurate as an inhibitor, and U.S. Pat. Nos. 4,472,562 and 4,472,563 employing acetylenic unsaturated inhibitors.
In copending application Ser. No. 07/354,557, filed May 22, 1989, now U.S. Pat. No. 5,015,691, one part heat curable organopolysiloxane compositions are described utilizing a platinum catalyst microencapsulated in an organic resin, such as a thermoplastic organic polymer, or a thermosetting organic polymer. The microencapsulated catalyst has an average diameter of about 4-60 microns. Although satisfactory shelf stability can be achieved under ambient conditions using such microencapsulated platinum catalysts in one part mixtures of vinyl-substituted diorganosiloxane fluid and siloxane hydride fluids, it has been found that the capsules often settle to the bottom of the one part heat curable organopolysiloxane mixture, or reduce the transparency of the curable mixture.
In copending application Ser. No. 424,022 filed 10-19-89, now U.S. Pat. No. 5,025,073, one part heat curable organopolysiloxane compositions are shown comprising a vinyl-substituted organopolysiloxane fluid, a siloxane hydride and an effective amount of an inclusion compound of a cyclodextrin with a platinum halide complex with a member selected from a cyclooctadiene and norbornadiene.
Although platinum has been found to be an effective hydrosilylation catalyst, other platinum metals, or salts thereof such as, rhodium and palladium, are constantly being evaluated to provide alternative hydrosilyation catalysts.